1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and an apparatus for the same, and more particularly, to wire bonding technique used in an assembly process of a semiconductor device.
2. Description of Related Art
In a wire bonding process of an assembly process of a semiconductor device, a semiconductor pellet and the inner leads formed in a lead frame are electrically connected by bonding wires. In a conventional wire bonding process, the following bonding methods are typically employed.
In a first conventional bonding method, a wire covered or coated by insulator is used as bonding wire. The insulator coated wire is constituted of, for example, gold (Au) wire 2 around which an insulation film 9 is coated, as shown in FIGS. 1A and 1B. In the first bonding, a ball formed on the tip portion of bonding wire is thermally pressed and adhered to a semiconductor pellet 3 using a capillary 1, as shown in FIG. 1A. The semiconductor pellet 3 has been adhered to an island 5 formed in the lead frame with Ag paste 4. In the second bonding, the bonding wire which is fed from a thin pore of the capillary 1 is thermally pressed and adhered to an inner lead 6 using the capillary 1, as shown in FIG. 1B. The inner lead 6 has been formed in the lead frame. The semiconductor pellet 3 and the inner lead 6 are electrically connected by above first bonding and second bonding.
In the method, in case of second bonding, if fusion of the insulation film 9 is insufficient, a portion of the insulation film 9 remains between the Au wire and the inner lead. In such a case, there is a problem in that it becomes easy for bonding wire to come off the inner lead.
Next, a second conventional bonding method is described in Japanese Laid Open Patent Disclosure (JP-A-Heil-105553). In this method, a Cu wire 10 is used as bonding wire, as shown in FIG. 2. The first bonding process and the second bonding process are performed in the same manner as in the above first conventional bonding method. After these processes, an oxidation film 11 is formed on the surface of Cu wire 10. According to the method, the short circuit between the bonding wires and the short circuit between the bonding wire and the semiconductor pellet can be avoided because the oxidation film 11 acts as the insulation film.
A third conventional bonding method is described in the above-mentioned reference (JP-A-Heil-105553). In the bonding method, an enamel film 12 is formed in place of the oxidation film 11 in the above second conventional bonding method, as shown in FIG. 3. That is, when the first bonding to an A1 pattern 13 of the semiconductor pellet 3 and the second bonding to the inner lead 6 are ended, enamel is applied to the surface of Cu wire 10 such that an enamel film 12 can be formed.
In the above second and third conventional bonding methods, there is a problem in that the manufacturing processes increase since the process for forming the oxidation film or enamel film is required in addition to the wire bonding processes.